1. Field of the Invention
The present invention relates to a field emission electron source for emitting electrons from a surface of a material by applying an electric field of an intensity higher than the work function of the material to the surface of the material and, more particularly, to a field emission electron source comprising electrodes and a semiconductor sandwiched between the two electrodes for emitting electrons by applying a voltage between the electrodes. The present invention also relates to a method of producing the same, and the use of the same.
2. Description of the Related Art
As field emission electron sources, those using the so-called Spindt type electrode such as disclosed in, for example, U.S. Pat. No. 3,665,241 are well known. The Spindt type electrode comprises a substrate having a multitude of minute emitter chips of a triangular pyramid shape disposed thereon and gate layers that have emission holes through which tips of the emitter chips are exposed and are insulated from the emitter chips. In this structure, a high voltage is applied in a vacuum atmosphere to the emitter chips as negative electrode with respect to the gate layer, electron beams can be emitted from the tips of the emitter chips through the emission holes.
However, the production process of the Spindt type electrode is complicated and it is difficult to make a multitude of emitter chips of a triangular pyramid shape with high accuracy and, hence difficult to make a device of large emission area when applying this technology to, for example, a planar light emitting apparatus or a display apparatus. Also with the Spindt type electrode, since the electric field is concentrated on the tip of the emitter chip, emitted electrons ionize various residual gases into positive ions where the degree of vacuum is low and the residual gas exists in the vicinity of the tips of the emitter chips. Therefore, the positive ions impinge on the tips of the emitter chips and eventually damage the tips of the emitter chips, resulting in such problems that the current density and efficiency of the emitted electrons become unstable and the service life of the emitter chips decreases. Thus, the Spindt type electrode has such a drawback that the atmosphere in which it is used must be pumped to a high degree of vacuum (10.sup.-5 Pa to 10.sup.-6 Pa) in order to avoid the problems described above, resulting in higher cost and difficult handling.
In order to overcome the drawback described above, field emission electron sources of MIM (Metal Insulator Metal) type and MOS (Metal Oxide Semiconductor) type have been proposed. The former is a field emission electron source of a planar configuration having a laminated structure of metal-insulation film-metal and the latter is one of a metal-oxide film-semiconductor structure. However, it is necessary to reduce the thickness of the insulation film or the oxide film in order to improve the electron emitting efficiency to thereby increase the number of electrons emitted with these types of field emission electron sources, while making the insulation film or the oxide film too thin may lead to dielectric breakdown when a voltage is applied between the upper and lower electrodes of the laminated structure described above. Thus there has been such a problem that, in order to avoid the dielectric breakdown of the insulator film, the electron emitting efficiency (pullout efficiency) cannot be made too high because there is a limitation on the reduction of the thickness of the insulation film or the oxide film.
A different field emission electron source has recently been proposed in Japanese Patent Kokai Publication No. 8-250766. According to this publication, the field emission electron source is made by using a single-crystal semiconductor substrate such as a silicon substrate, forming a porous semiconductor layer (a porous silicon layer, for example) by anodization of one surface of the semiconductor substrate, and forming a thin metal film on the porous semiconductor layer. A voltage is adapted to be applied between the semiconductor substrate and the thin metal film to cause the field emission electron source to emit electrons.
A display apparatus having the field emission electron source described above is also disclosed in Japanese Patent Kokai Publication No. 9-259795. In this case, when the silicon layer is made up of single-crystal, it is desirable that (100) direction is at right angle to a surface to enhance the efficiency of electron emission, because it is supposed that (100) porous silicon layer has holes of a diameter in the order of nano-meter and silicon crystal, which are arranged at right angle to the surface.
However, in the structure disclosed in Japanese Patent Kokai Publication No. 8-250766, since the substrate used therein uses a semiconductor substrate,.it is difficult to produce the device with a large area and to reduce the cost thereof.
In any event, both of the structure disclosed in Japanese Patent Kokai Publication No. 8-250766 and the structure disclosed in Japanese Patent Kokai Publication No. 9-259795, involve the so-called popping phenomenon during electron emission that leads to unevenness in the amount of electrons emitted, and therefore causes unevenness in the light emission when the field emission electron sources are applied to a planar light emitting apparatus or a display apparatus.